1. Field of the Invention
This invention is in the field of drawing crystalline bodies from a semiconductor melt using shaping parts which define the cross-sectional geometry of the crystalline body to be drawn. The shaping parts include a drawing nozzle which is inserted into the melt, whereby the feed of melt proceeds from a melt supply situated at the lower opening of the drawing nozzle, and is conveyed to the upper opening of the drawing nozzle due to capillary action.
2. Description of the Prior Art
The growth of crystals having a required cross-sectional shape such as tapes, tubes, threads and the like can only be accomplished upon employing shaping parts that function as drawing nozzles. One such method is known as the Stepanov process and is disclosed in the Bulletin of the Academy of Sciences of the USSR, Physical Series, No. 12, Vol. 33, 1969, pages 1775-1782 under the title "Transactions of the Second Conference on Producing Semiconductor Single Crystals by Stepanov's Method and on Prospects for Their Use in the Instrument-Making Industry".
The drawing of sillicon tapes for the purposes of solar cells, for example, can be carried out according to this method. To carry out the method, molten silicon is supplied in the gap of a drawing nozzle from a silicon reservoir. The melt meniscus is limited by the growing silicon crystal on the one hand and by an edge of the drawing nozzle lip on the other. The crystal growth thus becomes "edge-defined". The cross-sectional geometry of the crystal, particularly the thickness of the growing crystal tape, is thereby determined by the geometry of the drawing nozzle and by the distance between the crystallization front and the drawing nozzle, referred to as the meniscus height. Since the meniscus height can fluctuate within a certain range by reason of, for example, thermal disruptions, the cross-sectional shape of the growing crystal is thereby subject to fluctuations, although fundamentally defined by the geometry of the drawing nozzle. These fluctuations area unavoidable since maintaining the cross-sectional geometry of the crystal constant with fluctuations of the meniscus height is not possible with the edge-defined Stepanov process.
A further edge-defined growth process for crystalline bodies with predetermined cross section from the melt is known from DE-AS No. 19 35 372. Arbitrarily profiled crystalline bodies such as threads, tapes or tubes can be produced with this method by employing suitably shaped parts. The shaping parts consist of a material which can be moistened by the melt, and are equipped with capillary passages for the feed of the melt. They exhibit a horizontal, upper end surface on which a melt film can spread up to the sharp edges, the crystalline body being drawn from the melt film. The edge-limited, horizontal, upper end surface of the shaping part corresponds to the predetermined cross-sectional area of the crystalline body to be drawn. Due to fluctuations in the meniscus height, it is also difficult to keep the cross-sectional geometry of the crystal constant with this method.